Kenneth Biros (file image)
Kenneth Biros was convicted of a murder carried out in 1991
Ohio has become the first US state to carry out an execution with a single-drug injection instead of the usual combination of three drugs.
Kenneth Biros, 51, was put to death after the US Supreme Court denied his final appeal.
Biros had been convicted of the murder of a 22-year-old woman in 1991.
The new method was introduced because of concerns that prisoners could suffer extreme pain if the first of the usual three drugs failed to work effectively.
Critics say the method - which uses a dose of thiopental sodium and can take twice as long to take effect - is human experimentation. US justice officials deny this.
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